Because of their large data capacity, fiber optic cables are finding increasing application in telephony, computer systems and other applications where large amounts of information must be transmitted. However, unlike metal wires, fiber optic leds or cables are brittle and may break if bent beyond some bend radius. For bending radiuses greater than that at which cracking or breaking may occur, performance of the cable may still be degraded as a result of defraction within the leads caused by the bending. For example, the bend radius for breakage for fiber optic cables frequency used in telephony applications may be approximately 1/2 inch, but degradations in performance may occur at larger radiuses, starting at a bend radius of approximately 1". In the discussion to follow, the bend radius at which degradation becomes noticeable will sometimes be referred to as the "minimum bend radius".
Further, since a cable may be covered, or only selected fibers in a cable may break, such a break may not be detected until there has been loss of data; and the break may then be difficult to localize and may be both difficult and expensive to correct. It is, therefore, desirable when such cables are being handled, that suitable guides be provided to assure that the cable is not bent beyond its minimum bend radius.
One of the most likely locations for a break or other degradation in a fiber optic cable as a result of overbending is at the switching panels of a telephone central office. Typically, a large number of interconnect switching circuits or other types of circuits are mounted adjacent each other in a panel with cables extending from a selected side or sides of each of the circuits. In one application, there are six fiber optic cables extending from each circuit. Some of these cables maybe inputs and others outputs for the circuit and it is desirable that cables leaving a given circuit be able to extend toward either end of the panel to interconnect with other circuits on the panel or with circuits and locations external to the panel. However, to avoid undesirable signal degradations or breaks occurring in the cables, it is important in running the cables from the circuit board through the panel that the cables not be overbent at any point in their travel path. Existing systems for managing and controlling the running of fiber optic cables in a switching panel do not provide specific guides for assuring that cables are not overbent as they are run through the panel while allowing for multiple cables and multiple routing directions. Similar problems, also unresolved, may exist in various coaxial cable systems where characteristic impedance may be changed or wire or shielding cracked or broken if overbending occurs.
A need therefore exists for a cable guide for use with telephone central office switching panels and other circuit panels using fiber optic or other cables which may be damaged if overbent to manage and control the running of such cables in a manner so as to protect against overbending.